Fire Ant - Factoids

Excerpts from Steve Tvedten's book "The Best Control (2nd Edition)"
(Used here with permission.)

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Tribe Solenopsidini, Subfamily Mymicinae

Pest Species of Fire Ants — The “Ant from Hell”

There are many species of fire ants in the United States, but the most serious U. S.  fire ant pests are four in the genus Solenopsis: the Red Imported Fire Ant, the Black Imported Fire Ant, the Southern Fire Ant, and the native fire ant.  Distinguishing between imported and native species of fire ant is difficult, even for experts.  Identification usually requires 40 or more randomly collected worker ants for study.  The following sections briefly discuss the four fire ants of major concern in the U. S.  The Little Fire Ant is described later in the chapter.

Red Imported Fire Ant, Subfamily - Mymicinae

Introduced from western Brazil (Argentina or Paraguay), this fire ant species quickly and usually becomes the number one fire ant pest wherever it occurs.  The main reason for this is when it was introduced into the U. S. about 60 years ago its natural enemies were left behind in South America.  Since 1958, over 7,100 compounds have been evaluated for delayed toxicity against just this ant by the USDA Agricultural Research Service.  The Red Imported Fire Ant, Solenopsis invicta - (Buren), is associated with disturbed habitats, mostly created by humans, and is abundant in old fields, pastures, lawns, roadsides and many other open sunny areas.  It often inhabits fields used for agricultural purposes where its large above-ground mounds create problems in planting and harvesting crops.  John Morrison, Jr., et al, 1997, noted that Red Imported Ants will feed on wheat, corn and sorgham seed and to some extent on dry cotton and soybean seeds under laboratory conditions.  In areas where grass is periodically cut, mounds are flush with the ground and are hard to see.  This fire ant species is rarely found in mature forests and other areas with heavy shade, unless part of the area has been disturbed or opened by fire or storms.  Solenopsis invicta has the most toxic venom of all  U. S. fire ants.

The Red Imported Fire Ant builds mounds that are, on average, 10” - 24" in diameter and 18" high.  But larger fire ant mounds are not uncommon.  They also may extend 6' underground.  They also build soil tubes on foundations of buildings.  The primary function of mounds, beyond that of the simple ground nests of other ants, is microclimate regulation - controlling the temperature and humidity.  The ants can maintain a temperature inside the mound much higher than that outside, allowing them to continue colony growth even during cool weather.  They have a filtering system that admits only liquids into their digestive systems that even removes bacteria (e.g. Bacillus thurmingiensis) - so feed them sugar water with 1% boric acid or .5% Disodium Octoborate Tetrahydrate  for 8 weeks.  Originally it was incorrectly identified as Solenopsis saevissima richteri (Forel).

The fire ant mounds are symmetrical piles of excavated soil, rich in organic materials, laced with interconnected galleries and chambers.  The soil below ground also contains galleries and chambers.  During foraging periods only a small percentage of ants may be inside the mound; the rest are out gathering food.  That is why there are times of the day or night that flooding or drenching mounds are more effective.

A newly mated queen lays about a dozen eggs. When they hatch 7 to 10 days later, the larvae are fed by the queen. Later on, a queen fed by worker ants can lay up to 800 eggs per day. Larvae develop 6 to 10 days and then pupate. Adults emerge in 9 to 15 days. The average colony contains 100,000 to 500,000 workers and up to several hundred winged forms and queens. Queen ants can live 7 years or more, while worker ants generally live about 5 weeks, although they can survive much longer.

A newly established fire ant mound or nest rapidly produces young workers, and winged reproductives are produced for most of the year (8-10 months), much longer than the native species. Red imported fire ants quickly spread through a suitable habitat, and the species is now found throughout most of the southeastern United States and west into Texas and California (over 300,000,000 acres in the U.S.A.). They can and quickly do latch onto your flesh with barbed mandibles and sting repeatedly, pivoting in tiny circles until you, the victim can repel them or dies. The venom burns like a hot match and causes tiny blisters or white pustules that persist for days if left untreated or for weeks if scratched or infected and may leave permanent scars. Red imported fire ants have two types of colonies. Single-queen (monogyne form): only one queen per colony or mound; slightly larger workers; members of colonies are territorial; mound densities usually 20 - 80 mounds (up to 150 mounds) per acre; up to 7 million ants per acre. Multiple-queen (polygyne form): dozens of queens per colony; smaller average worker ants; colonies are interconnected; mound densities of 100 to 1000+ per acre; up to 40 million ants per acre.  Bait with raw fish, canned sausage, maple syrup (treated with boric acid or sodium borate 2% - 5%) or a combination of vitamin C and baking soda.

Black Imported Fire Ant

The Black Imported Fire Ant, Solenopsis richteri (Forel), is very similar to the Red Imported Fire Ant.  It is currently limited to a small area of northern Mississippi and Alabama.  It may be displaced from established habitats by the Red Fire Ant.  The Black Fire Ants come here from Argentina and/or Uruguay.

Scientists have long thought that the Black and Red Fire Ants were two distinct species.  Recently it has been discovered that hybrids of these ants produce viable offspring, and some scientists now wonder whether they are simply two races of the same species, varying only in color and perhaps behavior and/or have created hybrids.

Southern (California) Fire Ant

The Southern Fire Ant, Solenopsis xyloni, (McCook) is a native species that occurs from North Carolina south to northern Florida, along the Gulf Coast and west to California.  Colonies may be observed as mounds or more commonly may be constructed under the cover of stones, boards, and other objects or at the base of plants.  These ants also nest in wood or the masonry of houses, especially around heat sources such as fireplaces.  Nests often consist of loose soil with many craters scattered over 2 to 4 square feet.  In dry areas nests may be along streams, arroyos, and other shaded locations where soil moisture is high.  Southern fire ants usually swarm in late spring or summer.

Fire Ant (Tropical or Native fire ant)

The fire ant, Solenopsis geminata (Fabricus), is a native species sometimes called the Tropical Fire Ant.  This ant ranges from South Carolina to Florida and west to Texas.  Very similar to the Southern Fire Ant, this native fire ant usually nests in mounds constructed around clumps of vegetation, but may also nest under objects or in rotting wood.